Electroluminescent device

ABSTRACT

An electroluminescent element which includes host materials and guest materials in a part of an electroluminescent layer. Device characteristics (luminous efficiency, luminous characteristics, or the like) of an electroluminescent element are improved by using host materials and guest materials which have a common skeleton (represented by the following general formula) for an electroluminescent layer interposed between a pair of electrodes in the electroluminescent element. 
                         
In the common skeleton, X 1  to X 3 , each of which may be the same or different, are individually a hydrogen atom, a halogen atom, a lower alkyl group, an alkoxy group, an acyl group, a nitro group, a cyano group, an amino group, a dialkylamino group, a diarylamino group, a vinyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/754,973, filed Apr. 6, 2010, now U.S. Pat. No. 8,003,230, which is acontinuation of U.S. application Ser. No. 10/801,113, filed Mar. 16,2004, now U.S. Pat. No. 7,695,828, which claims the benefit of a foreignpriority application filed in Japan as Serial No. 2003-077875 on Mar.20, 2003, all of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electroluminescent element. Morespecifically, the invention relates to an electroluminescent elementhaving an electroluminescent layer, a part of which comprises hostmaterials and guest materials.

2. Related Art

An electroluminescent element comprises an electroluminescent layerinterposed between a pair of electrodes (anode and cathode). Theemission mechanism is as follows. Upon applying voltage through a pairof electrodes, holes injected from an anode and electrons injected froma cathode are recombined with each other within the electroluminescentlayer to lead the formation of molecular excitons, and the molecularexcitons return to the ground state while radiating energy to emitphoton. There are two excited states possible from organic compounds, asinglet state and a triplet state. It is considered that light emissioncan be obtained through both the singlet state and the triplet state.

Although an electroluminescent layer may have a single layer structurecomprising only a light-emitting layer formed by a light-emittingmaterial, the electroluminescent layer is formed to have not only asingle layer structure comprising only a light-emitting layer but also alamination layer structure comprising a hole injecting layer, a holetransporting layer, a hole blocking layer, an electron transportinglayer, an electron injecting layer, and the like which are formed by aplurality of functional material. Color tone can be appropriatelychanged by doping guest materials into host materials in thelight-emitting layer. There is some possibility of improving luminanceand lifetime of light emission in some combination of the host materialand the guest material.

It has been disclosed that the quantum efficiency or the durability isimproved of an electroluminescent element comprising host materials andguest materials, for example, tris(8-hydroxyquinoline)aluminum (alsoreferred to as Alq₃) as host materials and a coumarin derivative asguest materials. (For example, reference 1: Unexamined PatentPublication 2001-76876.)

In addition, it has been disclosed that an electroluminescent elementcomprising host materials and guest materials which is superior inluminous efficiency, durability, color purity characteristics, and thelike to those of the conventional electroluminescent element can beprovided by selecting host materials having the peak intensity ofemission spectrum in a certain range. (For example, reference 2:Unexamined Patent Publication 2001-118683.)

However, such electroluminescent element has been practicallyinsufficient yet in terms of luminous efficiency or luminouscharacteristics. It is desired to develop an electroluminescent elementhaving further superior device characteristics.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide an electroluminescent element having an electroluminescentlayer, a part of which comprises host materials and guest materials, andbeing superior in device characteristics such as luminous efficiency andluminous characteristics to those of the conventional electroluminescentelement.

The inventor discovers that the carrier transportation between hostmaterials and guest materials can be improved by using host materialsand guest materials which have a skeleton common to each other for anelectroluminescent element.

According to the present invention, device characteristics (luminousefficiency, luminous characteristics, or the like) of anelectroluminescent element is improved by using host materials and guestmaterials which have a skeleton common to each other for anelectroluminescent layer between a pair of electrodes of theelectroluminescent element.

Therefore, an electroluminescent element according to the inventioncomprises between a pair of electrodes host materials and guestmaterials which have in their molecules a common skeleton represented bythe following general formula (1), (9), and (14).

wherein R1 is a hydrogen atom, a lower alkyl group, an aryl group whichmay have a substituent, or a heterocyclic group which may have asubstituent, R2 to R5, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent, and Ar1 is an arylgroup which may have a substituent, or a heterocyclic group which mayhave a substituent.

wherein X1 to X4, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

wherein X1 to X3, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is an explanatory view for showing a device configuration of anelectroluminescent element according to Embodiment 1;

FIG. 2 is an explanatory view for showing a device configuration of anelectroluminescent element according to Embodiment 2;

FIG. 3 is an explanatory view for showing a device configuration of anelectroluminescent element according to Embodiment 3;

FIG. 4 is an explanatory view for showing a device configuration of anelectroluminescent element according to Example 1;

FIG. 5 is an explanatory view for showing a device configuration of anelectroluminescent element according to Example 2;

FIG. 6 is an explanatory view for showing a device configuration of anelectroluminescent element according to Example 3

FIG. 7 is a graph showing device characteristics of anelectroluminescent element;

FIG. 8 is a graph showing device characteristics of anelectroluminescent element;

FIG. 9 is a graph showing device characteristics of anelectroluminescent element;

FIG. 10 is a graph showing device characteristics of anelectroluminescent element;

FIGS. 11A and 11B are explanatory views for showing a light-emittingdevice; and

FIGS. 12A to 12G are explanatory views for showing electric appliances.

DESCRIPTION OF THE INVENTION

An electroluminescent element according to the present invention has thedevice configuration that an electroluminescent layer comprising a holetransporting layer and a light-emitting layer is interposed between apair of electrodes (an anode and a cathode). The light-emitting layercontains host materials and guest materials which have a common skeletonrepresented by general formulas (1), (9), and (14).

wherein R1 is a hydrogen atom, a lower alkyl group, an aryl group whichmay have a substituent, or a heterocyclic group which may have asubstituent, R2 to R5, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent, and Ar1 is an arylgroup which may have a substituent, or a heterocyclic group which mayhave a substituent.

In the invention, in case of using a compound which has an imidazoleskeleton represented by general formula (1) in a part of the molecularstructure for a light-emitting layer, both the host material and guestmaterials contained in the light-emitting layer are compounds having theimidazole skeleton. Specifically, host materials have a benzene ringrepresented by general formula (2) as a main skeleton, guest materialshave a coumarin skeleton represented by general formula (3) as a mainskeleton, at least one substituent out of substituents X1 to X6 in thehost material represented by general formula (2) and a substituent X1 inthe guest material represented by general formula (3) have an imidazoleskeleton represented by general formula (4).

wherein R1 is a hydrogen atom, a lower alkyl group, an aryl group whichmay have a substituent, or a heterocyclic group which may have asubstituent, and R2 to R5, each of which may be the same or different,are individually a hydrogen atom, a halogen atom, a lower alkyl group,an alkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

wherein R1 is a hydrogen atom, a lower alkyl group, an aryl group whichmay have a substituent, or a heterocyclic group, and R2 to R5, each ofwhich may be the same or different, are individually a hydrogen atom, ahalogen atom, a lower alkyl group, an alkoxy group, an acyl group, anitro group, a cyano group, an amino group, a dialkylamino group, adiarylamino group, a vinyl group which may have a substituent, an arylgroup which may have a substituent, or a heterocyclic group which mayhave a substituent.

wherein X1 to X4, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

In the invention, in case of using a compound, which has the structurerepresented by general formula (9) in a part of the molecular structure,for a light-emitting layer, both the host material and the guestmaterial are compounds (phenanthroline derivatives) having the structurerepresented by the general formula (9). Specifically, the host materialis a compound represented by general formula (10) and the guest materialis a compound represented by the general formula (11).

wherein Ar1 and Ar2, each of which may be the same or different, areindividually an aryl group which may have a substituent, or aheterocyclic group, and R1 and R2, each of which may be the same ordifferent, are individually a hydrogen atom, a halogen atom, a loweralkyl group, an alkoxy group, an acyl group, a nitro group, a cyanogroup, an amino group, a dialkylamino group, a diarylamino group, avinyl group which may have a substituent, an aryl group which may have asubstituent, or a heterocyclic group which may have a substituent.

wherein R1 to R8, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

wherein X1 to X3, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

In the invention, in case of using a compound which has the structurerepresented by general formula 14 in a part of the molecular structurefor a light-emitting layer, both the host material and the guestmaterial are compounds (carbazole derivatives) having the structurerepresented by the general formula (14).

As a lower alkyl group represented by general formulas (1) to (4), (9)to (11), and (14), a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, a sec-butyl group, a tert-butylgroup, a hexyl group, and the like are nominated, and those of whichhave preferably carbon atoms of from 1 to 6. An alkyl halide group suchas a trifluoromethyl group, or a cycloalkyl group such as a cyclohexylgroup may be used.

As an alkoxy group, a methoxy group, an ethoxy group, an n-propoxygroup, an isopropoxy group, an n-butoxy group, a sec-butoxy group, atert-butoxy group, a hexoxy group, and the like are nominated, and thoseof which have preferably carbon atoms of from 1 to 6. As an acyl group,an acetyl group is nominated.

As a dialkylamino group, a dimethylamino group, a diethylamino group,and the like are nominated, and those of which have preferably carbonatoms of from 1 to 4. As a diarylamino group, a diphenylamino group, abis(α-naphtyl)amino group are nominated. Alternatively, a substitutedarylamino group such as bis(m-tolyl)amino group may be used.

As a vinyl group, a vinyl group having a substituent such asdiphenylvinyl group may be used. As an aryl group, besides anonsubstituted aryl group such as a phenyl group or a naphthyl group, asubstituted aryl group such as an o-tolyl group, an m-tolyl group, ap-tolyl group, a xylyl group, a methoxyphenyl group, an ethoxyphenylgroup, a fluorophenyl group may be used. In addition, as a heterocyclicgroup, a pyridyl group, a furyl group, a thienyl group, and the like arenominated.

Further, a known material can be used for an electroluminescent layeraccording to the invention except a light-emitting layer comprising hostmaterials and guest materials which have a skeleton common to eachother. Either a small molecular material or a high molecular materialcan be used. Moreover, the material is composed of not only an organiccompound material but also an inorganic compound.

According to the invention, within an electroluminescent element havingthe configuration: anode/light-emitting layer/cathode, anode/holetransporting layer/light-emitting layer/cathode, anode/hole transportinglayer/light-emitting layer/electron transporting layer/cathode,anode/hole injecting layer/hole transporting layer/light-emittinglayer/electron transporting layer/cathode, anode/hole injectinglayer/hole transporting layer/light-emitting layer/electron transportinglayer/electron injecting layer/cathode, anode/hole injecting layer/holetransporting layer/light-emitting layer/hole blocking layer/electrontransporting layer/cathode, anode/hole injecting layer/hole transportinglayer/light-emitting layer/hole blocking layer/electron transportinglayer/electron injecting layer/cathode, or the like, a light-emittinglayer is formed by host materials and guest materials which have askeleton common to each other.

Hereinafter, embodiments of the invention will be explained in detail.

Embodiment 1

In Embodiment 1, the device configuration of an electroluminescentelement will be explained with reference to FIG. 1 in case of forming alight-emitting layer by host materials and guest materials which have askeleton common to each other.

As shown in FIG. 1, an electroluminescent element has the structurecomprising a substrate 100, a first electrode 101, an electroluminescentlayer 102, and a second electrode 103, sequentially.

As a material for the substrate 100, any material that is used for theconventional substrate can be used. For instance, a substrate formed byglass, quartz, transparent plastic, or the like can be used.

The first electrode 101 serves as an anode, and the second electrode 103serves as a cathode in Embodiment 1.

Therefore, the first electrode 101 is formed by an anode material. As ananode material, metals having a large work function (at least 4.0 eV),alloys, compounds having electrical conduction properties, and mixtureof these materials can be preferably used. As specific examples of theanode materials, besides ITO (indium tin oxide) or IZO (indium zincoxide) composed of indium oxide mixed with zinc oxide (ZnO) of from 2 to20%, aurum (Au), platinum (Pt), nickel (Ni), tungsten (W), chrome (Cr),molybdenum (Mo), ferrum (Fe), cobalt (Co), copper (Cu), palladium (Pd),nitride of metal material (TiN), or the like can be used.

On the other hand, as a cathode material for forming the secondelectrode 103, metals having a small work function (at most 3.8 eV),alloys, compounds having electrical conduction properties, and mixtureof these materials can be preferably used. As specific examples of thecathode materials, a transition metal containing a rare earth metal canbe used, besides an element in the first or second periodic row, thatis, an alkaline metal such as Li, Cs, or the like, alkaline earth metalsuch as Mg, Ca, Sr, or the like, alloys of these elements (Mg:Ag,Al:Li), or compounds (LiF, CsF, CaF₂). Alternatively, the secondelectrode 103 can be formed by a lamination layer of the transitionmetal and metals such as Al, Ag, or ITO (including alloys).

The above anode and cathode materials are deposited by vapor depositionor sputtering to form the first electrode 101 and the second electrode103. The electrodes are preferably formed to have a thickness of from 10to 500 nm.

An electroluminescent element according to the invention has thestructure that light generated by recombination of carries within anelectroluminescent layer emits from either the first electrode 101 orthe second electrode 103, or both electrodes. When light emits from thefirst electrode 101, the first electrode 101 is formed by a materialhaving light transmission properties. When light emits from the secondelectrode 103, the second electrode 103 is formed by a material havinglight transmission properties.

The electroluminescent layer 102 is formed by stacking a plurality oflayers. In Embodiment 1, the electroluminescent layer 102 is formed bystacking a hole transporting layer 111 and a light-emitting layer 112.

In this case, as a hole transportation material for forming the holetransporting layer 111, aromatic amine (that is, the one having abenzene ring-nitrogen bond) compounds are preferably used. For example,besides the above mentioned TPD, derivatives thereof such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereafter, α-NPD) iswidely used. Also used are star burst aromatic amine compounds,including 4,4′,4″-tris(N,N-diphenyl-amino)-triphenyl amine (hereafter,TDATA), and 4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine (hereafter, MTDATA).

As a material for forming the light-emitting layer 112, host materialsand guest materials which have a skeleton common to each otherrepresented by general formulas (1), (9), and (14). For instance, acombination of host materials represented by general formula (5) andguest materials represented by general formula (6) can be used.Preferably, a combination of host materials represented by generalformula (7) and guest materials represented by general formula (8), or acombination of host materials represented by general formula (12) andguest materials represented by general formula (13) can be used.

wherein R1 is a hydrogen atom, a lower alkyl group, an aryl group whichmay have a substituent, or a heterocyclic group which may have asubstituent, and R2 to R5, each of which may be the same or different,are individually a hydrogen atom, a halogen atom, a lower alkyl group,an alkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

wherein R1 is a hydrogen atom, a lower alkyl group, an aryl group whichmay have a substituent, or a heterocyclic group which may have asubstituent, R2 to R9, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent, R10 and R11 areindividually a hydrogen atom, a lower alkyl group, an aryl group whichmay have a substituent, or a heterocyclic group which may have asubstituent. R8 and R10, R9 and R11 may be bonded each other to form asubstituted or nonsubstituted saturated six-membered ring.

wherein R1 to R3, each of which may be the same or different, areindividually a hydrogen atom, an alkyl group, or an aryl group.

wherein R1 is a hydrogen atom, a lower alkyl group, an aryl group, or aheterocyclic group, R2 and R3, each of which may be the same ordifferent, are individually a hydrogen atom or a lower alkyl group, andR4 and R5, each of which may be the same or different, are individuallya hydrogen atom, a lower alkyl group, an aryl group which may have asubstituent, or a heterocyclic group which may have a substituent. R2and R4, R3 and R5 may be bonded each other to form a substituted ornonsubstituted saturated six-membered ring.

wherein R1 and R2, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

wherein R1 to R8, each of which may be the same or different, areindividually a hydrogen atom, a halogen atom, a lower alkyl group, analkoxy group, an acyl group, a nitro group, a cyano group, an aminogroup, a dialkylamino group, a diarylamino group, a vinyl group whichmay have a substituent, an aryl group which may have a substituent, or aheterocyclic group which may have a substituent.

Embodiment 2

In Embodiment 2, the device configuration of an electroluminescentelement in case that an electroluminescent layer has a differentlamination structure from that explained in Embodiment 1 will beexplained with reference to FIG. 2.

A substrate, a first electrode, and a second electrode are formed by thesame material and the same procedure as those described in Embodiment 1.Through this embodiment, like components are denoted by like numerals asof Embodiment 1 and will not be further explained.

An electroluminescent layer 202 according to Embodiment 2 has alamination structure comprising a hole transporting layer 211, alight-emitting layer 212, and an electron transporting layer 213.

A material for forming the hole transporting layer 211 is the same asthat for forming the hole transporting layer 111, and will not befurther explained.

A material for forming a light-emitting layer 212 is also the same asthat for forming the light-emitting layer 112, and will not be furtherexplained.

As an electron transportation material for forming an electrontransporting layer 213, a metal complex having a quinoline skeleton or abenzoquinoline skeleton such as Alq₃, Almq₃, BeBq₂, or a mixed ligandcomplex such as Balq₃ is preferably used. Alternatively, a metal complexhaving an oxazole or thiazole ligand such as Zn(BOX)₂ or Zn(BTZ)₂ can beused. Besides, oxadiazole derivatives such as2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviatedPBD), and 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(hereinafter, OXD-7); triazole derivatives such as3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(hereinafter, TAZ) and3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(hereinafter, p-EtTAZ); and phenanthroline derivatives such asbathophenanthroline (hereinafter, BPhen) and bathocuproin (hereinafter,BCP) can be used in addition to metal complexes.

Embodiment 3

In Embodiment 3, the device configuration of an electroluminescentelement in which a sequence of lamination of an electroluminescent layeris different from that descried in Embodiments 1 and 2 will be explainedwith reference to FIG. 3.

A substrate, a first electrode, and a second electrode are formed by thesame material and the same procedure as those described in Embodiment 1.Through this embodiment, like components are denoted by like numerals asof Embodiment 1 and will not be further explained.

An electroluminescent layer 302 has a single layer structure comprisingonly a light-emitting layer 311.

A light-emitting layer 311 according to Embodiment 3 can be formed byhost materials and guest materials which have a skeleton common to eachother represented by general formula (14). Preferably, thelight-emitting layer 311 can be formed by host materials represented bythe following structural formula (15) and guest materials represented bythe following formula (16).

In Embodiment 3, since an electroluminescent layer 302 comprises onlylight-emitting layer 311, host materials and guest materials, each ofwhich have both hole transportation properties and electrontransportation properties as mentioned above are preferably used.

The structure of the electroluminescent layer described in Embodiments 1to 3 is not limited to the above mentioned structure, a hole injectinglayer, a hole blocking layer, or the like can be appropriately combinedtherewith.

In this instance, as a hole injection material for forming a holeinjecting layer, porphyrin compounds are useful among other organiccompounds such as phthalocyanine (hereinafter, H₂—Pc), copperphthalocyanine (hereinafter, Cu—Pc), or, the like. Further,chemical-doped conductive polymer compounds can be used, such aspolyethylene dioxythipophene (hereinafter, PEDOT) doped with polystyrenesulfonate (hereinafter, PSS), polyaniline, polyvinyl carbazole(hereinafter, PVK), or the like.

As a material having hole blocking properties for forming a holeblocking properties, 1,3,4-oxadiazole derivatives such as2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (hereinafter, PBD),bathocuproin (abbreviated BCP), 1,2,4-triazole derivatives such as5-(4-biphenylyl)-3-(4-tert-butylphenyl)-4-phenyl-1,2,4-triazole(hereinafter, TAZ), or the like can be used.

EXAMPLES

Hereinafter, examples according to the present invention will beexplained.

Example 1

In this example, an electroluminescent element that is formed by usinghost materials and guest materials which have a skeleton common to eachother, for a light-emitting layer, and an electroluminescent layer thathas the configuration, as described in Embodiment 1, comprising at leasta hole transporting layer and a light-emitting layer will be explainedwith reference to FIG. 4.

Firstly, a first electrode 401 of an electroluminescent element isformed over substrate 400. In this example, the first electrode servesas an anode. The first electrode 401 is formed by ITO to have athickness of 110 nm by sputtering.

Secondly, an electroluminescent layer 402 is formed over the firstelectrode (anode) 401. In this example, the electroluminescent layer 402has a lamination structure comprising a hole injection layer 411, a holetransporting layer 412, and a light-emitting layer 413. Thelight-emitting layer 413 is formed by host materials represented by thefollowing structural formula (17) and guest materials represented by thefollowing structural formula (18) as host materials and guest materialswhich have a common skeleton represented by the general formula (1).

Further, compounds represented by the following structural formula (19)can be used besides the host material represented by the structuralformula (17).

In addition, compounds represented by the following structural formulas(20) to (22) can be used besides the guest material represented by thestructural formula (18).

Besides, the light-emitting layer 413 can be formed by host materialsrepresented by the following structural formula (23) and guest materialsrepresented by the following structural formula (24) as host materialsand guest materials which have a common skeleton represented by thegeneral formula (9).

Further, compounds represented by the following structural formula (25)can be used besides the host material represented by the structuralformula (23).

In addition, compounds represented by the following structural formula(26) can be used besides the guest material represented by thestructural formula (24).

Besides, the light-emitting layer 413 can be formed by host materialsrepresented by the following structural formula (15) and guest materialsrepresented by the following structural formula (16) as host materialsand guest materials which have a common skeleton represented by thegeneral formula (14).

A substrate provided with the first electrode 401 is secured with asubstrate holder of a commercial vacuum deposition system in such a waythat the surface provided with the first electrode 401 is down. Then,copper phthalocyanine (hereinafter, Cu—Pc) is put into an evaporationsource installed in the internal of the vacuum deposition system. Andthen, the hole injecting layer 411 is formed to have a thickness of 20nm by vacuum vapor deposition with a resistive heating method.

The hole transporting layer 412 having excellent hole transportationproperties is formed by 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl(hereafter, α-NPD) to have a thickness of 30 nm in accordance with thesame procedure as that conducted for forming the hole injection layer411.

The light-emitting layer 413 is formed, in this example, by the hostmaterial represented by the structural formula (17) and the guestmaterial represented by the structural formula (18) by co-evaporation tohave a thickness of 20 nm.

A second electrode 403 serving as a cathode is formed. In this example,the second electrode 403 is formed to have a lamination structure bydepositing calcium fluoride (CaF) to have a thickness of 2 nm by vapordeposition over the electroluminescent layer 402, and aluminum (Al) isdeposited to have a thickness of 100 nm by sputtering thereon.

Accordingly, an electroluminescent element having the light-emittinglayer 413 comprising host materials and guest materials which have askeleton common to each other is formed. The configuration described inExample 1 is a single hetero structure in which the electroluminescentlayer 402 comprises the hole transporting layer 412 and thelight-emitting layer 413. Since each the host material and the guestmaterial is a compound having common skeletons, the electroluminescentelement having excellent carrier transportation properties, andexcellent device characteristics such as luminance characteristics andcurrent-voltage characteristics can be formed.

In this example, the case that the first electrode 401 is formed overthe substrate by an anode material to serve as an anode is described;however, the present invention is not limited thereto. The firstelectrode 401 can be formed by a cathode material to serve as a cathode.In this case, that is, in case of exchanging an anode to a cathode, asequence of lamination of the electroluminescent layer described in thisexample is reversed. In this example, the first electrode (anode) 401 isa transparent electrode in order to extract light generated in theelectroluminescent layer 402 from the first electrode (anode) 401;however, the invention is not limited thereto. If the second electrode(cathode) 403 is formed by a selected material that is suitable forsecuring transmittance, light can be extracted from the cathode.

Example 2

In this example, an electroluminescent element that is formed by usinghost materials and guest materials which have a common skeleton for alight-emitting layer, and an electroluminescent layer that has theconfiguration described in Embodiment 2 comprising at least a holetransporting layer, a light-emitting layer, and an electron transportinglayer will be explained with reference to FIG. 5.

A configuration in Example 2 is similar to that described in Example 1.The configuration in Example 2 is distinguished from that in Example 1by the fact that an electroluminescent layer 502 comprises at least anelectron transporting layer 514.

That is, a first electrode 501, a hole injection layer 511, a holetransporting layer 512, a light-emitting layer 513, and a secondelectrode 503 can be formed by the same materials as those used inExample 1 to have the same thicknesses as those of the configurationdescribed in Example 1 as shown in FIG. 5.

The electron transporting layer 514 is formed by vapor deposition tohave a thickness of 20 nm by the compound represented by the structuralformula 19 that is used as the host material for the light-emittinglayer 513. Further, the carrier transportation properties can beimproved by using the same compounds for both the light-emitting layer513 and the electron transporting layer 514.

The configuration described in Example 2 has a double hetero structurethat is unlike in the case of Example 1 explaining a single heterostructure.

Example 3

In this example, an electroluminescent element that is formed by usinghost materials and guest materials which have a common skeleton for alight-emitting layer, and an electroluminescent layer that has theconfiguration described in Embodiment 3 comprising at least alight-emitting layer will be explained with reference to FIG. 6.

A configuration in Example 3 is distinguished from those in Examples 1and 2 by the fact that an electroluminescent layer comprises at least alight-emitting layer 613.

A first electrode 601 and a second electrode 603, which are formed overa substrate 600, can be formed by the same materials as those used inExample 1 to have the same thicknesses as those of the configurationdescribed in Example 1 as shown in FIG. 6.

In case of this example, the light-emitting layer 613 is required to beformed by a material having hole transportation properties and electrontransportation properties since the electroluminescent layer is composedof only the light-emitting layer 613. Specifically, the host materialand the guest material which have a common skeleton represented by thegeneral formula (14) can be used as the light-emitting layer 613. Forinstance, the host material 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP)represented by the structural formula (15) and the guest material(BCzVBi) represented by the structural formula (16) are dispersed intosolvent (dichloroethane, or the like) in 1:0.3 molar ratio to be coatedfor forming the light-emitting layer 613.

As noted above, the electroluminescent layer 602 according to thisexample is formed.

Example 4

In this example, an electroluminescent element which has the deviceconfiguration described in Example 2: ITO/Cu—Pc (20 nm)/α-NPD (30nm)/TPBI+coumarin 30 (30 nm)/TPBI (30 nm)/CaF (2 nm)/Al wasmanufactured. Then, the device characteristics of the electroluminescentdevice were measured. The size of an electrode formed by ITO is2-mm-square. The electroluminescent element exhibits blue emissionhaving an emission spectrum with maximum intensity at 475 nm, CIE (x,y)=(0.152, 0.302) in a wavelength region.

Each plot 2 in FIGS. 7 to 10 shows the measurement results. Theluminance-current characteristics plot 2 in FIG. 7 shows that aluminance of approximately 3100 cd/m² is obtained at a current densityof 100 mA/cm².

The luminance-voltage characteristics plot 2 in FIG. 8 shows that aluminance of approximately 1600 cd/m² is obtained at an applied voltageof 8 V.

The current efficiency-luminance characteristics plot 2 in FIG. 9 showsthat a current efficiency is approximately 5.1 cd/A at a luminance ofapproximately 100 cd/m².

The current-voltage characteristics plot 2 in FIG. 10 shows that acurrent flow is approximately 0.66 mA at an applied voltage of 7 V.

Comparative Example 1

On the other hand, an electroluminescent element in which bathocuproin(hereinafter, BCP), which has been used as host materials for anelectroluminescent element, is used for forming an electron transportinglayer, and as host materials for an electroluminescent layer wasmeasured. The electroluminescent element has the device configuration:ITO/Cu—Pc (20 nm)/α-NPD (30 nm)/BCP+coumarin 30 (30 nm)/BCP (30 nm)/CaF(2 nm)/Al. Each plot 1 in FIGS. 7 to 10 shows the measurement results.The luminance-current characteristics plot 1 in FIG. 7 shows that aluminance of approximately 1800 cd/m² is obtained at a current densityof 100 mA.

The luminance-voltage characteristics plot 1 in FIG. 8 shows that aluminance of approximately 50 cd/m² is obtained at an applied voltage of8 V. The result provides the fact that the luminance to an appliedvoltage is significantly decreased compared with that of the deviceconfiguration shown in Example 2.

The current efficiency-luminance characteristics plot 1 in FIG. 9 showsthat a current efficiency is approximately 3.5 cd/A at a luminance ofapproximately 100 cd/cm². Also in this case the current efficiency isworse than that represented by plot 2 of the device configuration shownin Example 2.

The current-voltage characteristics plot 1 in FIG. 10 shows that currentflow is only approximately 0.02 mA at an applied voltage of 7 V.

From the comparative results described above, the device configurationcan be improved by forming the electroluminescent element using hostmaterials and guest materials which have a common skeleton according tothe invention.

Example 5

In this example, a light-emitting device having an electroluminescentelement according to the present invention in a pixel portion will beexplained with reference to FIG. 11. FIG. 11A is a top view of alight-emitting device. FIG. 11B is a cross-sectional view of FIG. 11Ataken along the line A-A′. Reference numeral 901 by a dotted linedenotes a driver circuit unit (a source side driver circuit); referencenumeral 902 denotes a pixel portion; 903, a driver circuit unit (a gateside driver circuit); 904, a sealing substrate; and 905, sealing agent.The inside portion surrounded by the sealing agent 905 is space 907.

Reference 908 denotes a wiring for transmitting signals inputted to thesource signal line driver circuit 901 and the gate signal line drivercircuit 903. The wiring receives video signals, clock signals, startsignals, or reset signals from an FPC (flexible printed circuit) 909serving as an external input terminal. Although only FPC is illustratedin the drawing, a PWB (printed wirings board) may be attached to theFPC. As used in this specification, the term “light-emitting device”refers to not only a main body of a light-emitting device but also themain body provided with the FPC 909 or PWB.

Then, a cross-sectional structure will be explained with reference toFIG. 11B. A driver circuit and a pixel portion are formed over asubstrate 910. In FIG. 11B, the source side driver circuit 901 as adriver circuit unit and the pixel portion 902 are illustrated.

The source signal line driver circuit 901 is provided with a CMOScircuit formed by combining an n-channel TFT 923 and a p-channel TFT924. A TFT for forming a driver circuit may be formed by a known CMOS,PMOS, or NMOS circuit. In this example, a driver integrated type inwhich a driver circuit is formed over a substrate is described, but notexclusively, the driver circuit can be formed outside instead of over asubstrate.

The pixel portion 902 is composed of a plurality of pixels including aswitching TFT 911, a current control TFT 912, and a first electrode 913connected electrically to the drain of the current control TFT 912.Further, an insulator 914 is formed to cover the edge of the firstelectrode 913. Here, the insulator 914 is formed by a positive typephotosensitive acrylic resin film.

In order to make favorable coverage, an upper edge portion and a loweredge portion of the insulator 914 are formed to have a curved facehaving a radius of curvature. For example, positive type photosensitiveacrylic is used as a material for the insulator 914, only upper edgeportion of the insulator 914 is preferably having a radius of curvature(from 0.2 to 3 μm). As the insulator 914, either a negative typephotosensitive resin that becomes insoluble to etchant by light or apositive type photosensitive resin that becomes dissoluble to etchant bylight can be used.

An electroluminescent layer 916 and a second electrode 917 are formedover the first electrode 913, respectively. As a material for the firstelectrode 913 serving as an anode, a material having a large workfunction is preferably used. For instance, the first electrode can beformed by a single layer such as an ITO (indium tin oxide) film, an IZO(indium zinc oxide) film, a titanium nitride film, a chromic film, atungsten film, a Zn film, or a Pt film; a lamination layer comprisingone of the above single layer and a film containing mainly titaniumnitride and aluminum; a three lamination layer comprising a titaniumfilm, a film containing aluminum as its main components, and a titaniumnitride; or the like. In case of adopting the lamination layer, thefirst electrode can be formed to have a low resistance as a wiring, andmake good ohmic contact, and serve as an anode.

The electroluminescent layer 916 is formed by vapor deposition using anevaporation mask or ink jetting. The electroluminescent layer 916contains host materials and guest materials which have a commonskeleton. As a material for using together with the host material andthe guest material, either small molecular materials or high molecularmaterials can be used. In addition, as a material for anelectroluminescent layer, a single layer or a lamination layer formed byan organic compound is generally used. However, the inventioncomprehends the case that a part of a film formed by an organic compoundincludes an inorganic compound.

As a material for the second electrode (cathode) 917 formed over theelectroluminescent layer 916, a material having a small work function(Al, Ag, Li, Ca, or alloys of these elements such as MgAg, MgIn, AlLi,CaF₂, or CaN) can be used. In case of extracting light generated in theelectroluminescent layer 916 from the second electrode (cathode) 917,the second electrode (cathode) 917 is preferably formed by a laminationlayer comprising a thin metal film and a transparent conductive film(alloys such as indium tin oxide (ITO), indium zinc oxide (In₂O₃—ZnO),zinc oxide (ZnO), or the like).

The sealing substrate 904 is pasted onto the substrate 910 with thesealing agent 905 to encapsulate an electroluminescent element 918within the space 907 surrounded by the substrate 910, the sealingsubstrate 904, and the sealing agent 905. The invention comprehends notonly the case that the space 907 is filled with inert gases (such asnitrogen or argon) but also the case that the space 907 is filled withthe sealing agent 905.

The sealing agent 905 is preferably formed by epoxy-based resin. Inaddition, it is desirable that the material for the sealing agentinhibits the penetration of moisture or oxygen. As a material for thesealing substrate 904, a plastic substrate such as FRP(fiberglass-reinforced plastics), PVF (poly(vinyl fluoride), Myler,polyester, or acrylic can be used besides a glass substrate or a quartzsubstrate.

Accordingly, a light-emitting device having an electroluminescentelement according to the invention can be obtained.

The light-emitting device described in this example can be practiced bycombining freely with the configuration of the electroluminescentelement explained in Examples 1 to 3.

Example 6

Various electric appliances completed by using a light-emitting devicehaving an electroluminescent element according to the present inventionwill be explained in this example.

Given as examples of such electric appliances manufactured by using alight-emitting device having the electroluminescent element according tothe invention: a video camera, a digital camera, a goggles-type display(head mount display), a navigation system, a sound reproduction device(a car audio equipment, an audio set and the like), a laptop personalcomputer, a game machine, a portable information terminal (a mobilecomputer, a cellular phone, a portable game machine, an electronic book,or the like), an image reproduction device including a recording medium(more specifically, a device which can reproduce a recording medium suchas a digital versatile disc (DVD) and so forth, and includes a displayfor displaying the reproduced image), or the like. FIGS. 12A to 12G showvarious specific examples of such electric appliances.

FIG. 12A illustrates a display device which includes a frame 2001, asupport table 2002, a display portion 2003, a speaker portion 2004, avideo input terminal 2005, or the like. The light-emitting device havingthe electroluminescent element according to the invention can be usedfor the display portion 2003. The display device is including all of thedisplay devices for displaying information, such as a personal computer,a receiver of TV broadcasting, and an advertising display.

FIG. 12B illustrates a laptop computer which includes a main body 2201,a casing 2202, a display portion 2203, a keyboard 2204, an externalconnection port 2205, a pointing mouse 2206, or the like. Thelight-emitting device having the electroluminescent element according tothe invention can be used to the display portion 2203.

FIG. 12C illustrates a mobile computer which includes a main body 2301,a display portion 2302, a switch 2303, an operation key 2304, aninfrared port 2305, or the like. The light-emitting device having theelectroluminescent element according to the invention can be used to thedisplay portion 2302.

FIG. 12D illustrates an image reproduction device including a recordingmedium (more specifically, a DVD reproduction device), which includes amain body 2401, a casing 2402, a display portion A 2403, another displayportion B 2404, a recording medium (DVD or the like) reading portion2405, an operation key 2406, a speaker portion 2407, or the like. Thedisplay portion A 2403 is used mainly for displaying image information,while the display portion B 2404 is used mainly for displaying characterinformation. The light-emitting device having the electroluminescentelement according to the invention can be used to the display portion A2403 and the display portion B 2404. Note that the image reproductiondevice with a recording medium further includes a domestic game machineor the like.

FIG. 12E illustrates a goggle type display (head mounted display), whichincludes a main body 2501, a display portion 2502, and an arm portion2503. The light-emitting device having the electroluminescent elementaccording to the invention can be used to the display portion 2502.

FIG. 12F illustrates a video camera which includes a main body 2601, adisplay portion 2602, an casing 2603, an external connecting port 2604,a remote control receiving portion 2605, an image receiving portion2606, a battery 2607, a sound input portion 2608, an operation key 2609,an eyepiece portion 2610, or the like. The light-emitting device havingthe electroluminescent element according to the invention can be used tothe display portion 2602.

FIG. 12G illustrates a cellular phone which includes a main body 2701, acasing 2702, a display portion 2703, a sound input portion 2704, a soundoutput portion 2705, an operation key 2706, an external connecting port2707, an antenna 2708, or the like. The light-emitting device having theelectroluminescent element according to the invention can be used to thedisplay portion 2703.

As set forth above, the light-emitting device having theelectroluminescent element according to the invention can be appliedvariously to a wide range of electric appliances in all fields. Byapplying the light-emitting device to electric appliances in variousfields', low power consumption and long lifetime can be achieved.

An electroluminescent element that is superior in device characteristicssuch as emission efficiency, luminous characteristics, or the like, tothe conventional electroluminescent element by manufacturing in such away that a part of an electroluminescent layer is formed by hostmaterials and guest materials which have a common skeleton.

What is claimed is:
 1. An electroluminescent element comprising: a pairof electrodes; and a light-emitting layer comprising a host material anda guest material which have a carbazole skeleton common to each otherbetween the pair of electrodes, wherein one of the 3-position and the6-position in the carbazole skeleton is a hydrogen atom, wherein theother of the 3-position and the 6-position in the carbazole skeleton isa hydrogen atom, a halogen atom, lower alkyl group, an alkoxy group, anacyl group, a nitro group, a cyano group, an amino group, a dialkylaminogroup, a diarylamino group, a substituted or unsubstituted vinyl group,a substituted or unsubstituted aryl group, or a substituted orunsubstituted heterocyclic group, wherein the 9-position in thecarbazole skeleton is a hydrogen atom, a halogen atom, an alkoxy group,an acyl group, a nitro group, a cyano group, an amino group, adialkylamino group, a diarylamino group, or a substituted orunsubstituted heterocyclic group, wherein the guest material has onecarbazole skeleton, and wherein the guest material emits light.
 2. Theelectroluminescent element according to claim 1, wherein each of thehost material and the guest material has both hole transportationproperty and electron transportation property.
 3. A light-emittingdevice comprising the electroluminescent element according to claim 1.4. A light-emitting device comprising the electroluminescent elementaccording to claim
 2. 5. An electric appliance comprising thelight-emitting device according to claim
 3. 6. An electric appliancecomprising the light-emitting device according to claim
 4. 7. Theelectroluminescent element according to claim 1, further comprising atleast one of a hole transporting layer and an electron transportinglayer.
 8. The electroluminescent element according to claim 7, wherein amaterial of the hole transporting layer is an aromatic amine.
 9. Theelectroluminescent element according to claim 7, wherein a material ofthe electron transporting layer is selected from a metal complex havinga quinoline skeleton, a metal complex having benzoquinoline skeleton, ametal complex having an oxazole ligand, a metal complex having athiazole ligand, an oxadiazole derivative, a triazole derivative, and aphenanthroline derivative.